clone: prepare to recycle CLONE_STOPPED

Ulrich says that we never used this clone flags and that nothing should be
using it.

As we're down to only a single bit left in clone's flags argument, let's add a
warning to check that no userspace is actually using it.  Hopefully we will
be able to recycle it.

Roland said:

  CLONE_STOPPED was previously used by some NTPL versions when under
  thread_db (i.e.  only when being actively debugged by gdb), but not for a
  long time now, and it never worked reliably when it was used.  Removing it
  seems fine to me.

[[email protected]: it looks like CLONE_DETACHED is being used]
Cc: Ulrich Drepper <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Roland McGrath <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/fork.c

@@ -1450,6 +1450,23 @@ long do_fork(unsigned long clone_flags,
 	int trace = 0;
 	long nr;
 
+	/*
+	 * We hope to recycle these flags after 2.6.26
+	 */
+	if (unlikely(clone_flags & CLONE_STOPPED)) {
+		static int __read_mostly count = 100;
+
+		if (count > 0 && printk_ratelimit()) {
+			char comm[TASK_COMM_LEN];
+
+			count--;
+			printk(KERN_INFO "fork(): process `%s' used deprecated "
+					"clone flags 0x%lx\n",
+				get_task_comm(comm, current),
+				clone_flags & CLONE_STOPPED);
+		}
+	}
+
 	if (unlikely(current->ptrace)) {
 		trace = fork_traceflag (clone_flags);
 		if (trace)